src/librustc_typeck/check/expr.rs

   1 //! Type checking expressions.
   2 //!
   3 //! See `mod.rs` for more context on type checking in general.
   4
   5 use crate::check::BreakableCtxt;
   6 use crate::check::cast;
   7 use crate::check::coercion::CoerceMany;
   8 use crate::check::Diverges;
   9 use crate::check::FnCtxt;
  10 use crate::check::Expectation::{self, NoExpectation, ExpectHasType, ExpectCastableToType};
  11 use crate::check::fatally_break_rust;
  12 use crate::check::report_unexpected_variant_res;
  13 use crate::check::Needs;
  14 use crate::check::TupleArgumentsFlag::DontTupleArguments;
  15 use crate::check::method::{probe, SelfSource, MethodError};
  16 use crate::util::common::ErrorReported;
  17 use crate::util::nodemap::FxHashMap;
  18 use crate::astconv::AstConv as _;
  19
  20 use errors::{Applicability, DiagnosticBuilder, pluralize};
  21 use syntax_pos::hygiene::DesugaringKind;
  22 use syntax::ast;
  23 use syntax::symbol::{Symbol, kw, sym};
  24 use syntax::source_map::Span;
  25 use syntax::util::lev_distance::find_best_match_for_name;
  26 use rustc::hir;
  27 use rustc::hir::{ExprKind, QPath};
  28 use rustc::hir::def_id::DefId;
  29 use rustc::hir::def::{CtorKind, Res, DefKind};
  30 use rustc::hir::ptr::P;
  31 use rustc::infer;
  32 use rustc::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  33 use rustc::middle::lang_items;
  34 use rustc::mir::interpret::GlobalId;
  35 use rustc::ty;
  36 use rustc::ty::adjustment::{
  37     Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability,
  38 };
  39 use rustc::ty::{AdtKind, Visibility};
  40 use rustc::ty::Ty;
  41 use rustc::ty::TypeFoldable;
  42 use rustc::ty::subst::InternalSubsts;
  43 use rustc::traits::{self, ObligationCauseCode};
  44
  45 use rustc_error_codes::*;
  46
  47 use std::fmt::Display;
  48
  49 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  50     fn check_expr_eq_type(&self, expr: &'tcx hir::Expr, expected: Ty<'tcx>) {
  51         let ty = self.check_expr_with_hint(expr, expected);
  52         self.demand_eqtype(expr.span, expected, ty);
  53     }
  54
  55     pub fn check_expr_has_type_or_error(
  56         &self,
  57         expr: &'tcx hir::Expr,
  58         expected: Ty<'tcx>,
  59         extend_err: impl Fn(&mut DiagnosticBuilder<'_>),
  60     ) -> Ty<'tcx> {
  61         self.check_expr_meets_expectation_or_error(expr, ExpectHasType(expected), extend_err)
  62     }
  63
  64     fn check_expr_meets_expectation_or_error(
  65         &self,
  66         expr: &'tcx hir::Expr,
  67         expected: Expectation<'tcx>,
  68         extend_err: impl Fn(&mut DiagnosticBuilder<'_>),
  69     ) -> Ty<'tcx> {
  70         let expected_ty = expected.to_option(&self).unwrap_or(self.tcx.types.bool);
  71         let mut ty = self.check_expr_with_expectation(expr, expected);
  72
  73         // While we don't allow *arbitrary* coercions here, we *do* allow
  74         // coercions from ! to `expected`.
  75         if ty.is_never() {
  76             assert!(!self.tables.borrow().adjustments().contains_key(expr.hir_id),
  77                     "expression with never type wound up being adjusted");
  78             let adj_ty = self.next_diverging_ty_var(
  79                 TypeVariableOrigin {
  80                     kind: TypeVariableOriginKind::AdjustmentType,
  81                     span: expr.span,
  82                 },
  83             );
  84             self.apply_adjustments(expr, vec![Adjustment {
  85                 kind: Adjust::NeverToAny,
  86                 target: adj_ty
  87             }]);
  88             ty = adj_ty;
  89         }
  90
  91         if let Some(mut err) = self.demand_suptype_diag(expr.span, expected_ty, ty) {
  92             let expr = expr.peel_drop_temps();
  93             self.suggest_ref_or_into(&mut err, expr, expected_ty, ty);
  94             extend_err(&mut err);
  95             // Error possibly reported in `check_assign` so avoid emitting error again.
  96             err.emit_unless(self.is_assign_to_bool(expr, expected_ty));
  97         }
  98         ty
  99     }
 100
 101     pub(super) fn check_expr_coercable_to_type(
 102         &self,
 103         expr: &'tcx hir::Expr,
 104         expected: Ty<'tcx>
 105     ) -> Ty<'tcx> {
 106         let ty = self.check_expr_with_hint(expr, expected);
 107         // checks don't need two phase
 108         self.demand_coerce(expr, ty, expected, AllowTwoPhase::No)
 109     }
 110
 111     pub(super) fn check_expr_with_hint(
 112         &self,
 113         expr: &'tcx hir::Expr,
 114         expected: Ty<'tcx>
 115     ) -> Ty<'tcx> {
 116         self.check_expr_with_expectation(expr, ExpectHasType(expected))
 117     }
 118
 119     pub(super) fn check_expr_with_expectation(
 120         &self,
 121         expr: &'tcx hir::Expr,
 122         expected: Expectation<'tcx>,
 123     ) -> Ty<'tcx> {
 124         self.check_expr_with_expectation_and_needs(expr, expected, Needs::None)
 125     }
 126
 127     pub(super) fn check_expr(&self, expr: &'tcx hir::Expr) -> Ty<'tcx> {
 128         self.check_expr_with_expectation(expr, NoExpectation)
 129     }
 130
 131     pub(super) fn check_expr_with_needs(&self, expr: &'tcx hir::Expr, needs: Needs) -> Ty<'tcx> {
 132         self.check_expr_with_expectation_and_needs(expr, NoExpectation, needs)
 133     }
 134
 135     /// Invariant:
 136     /// If an expression has any sub-expressions that result in a type error,
 137     /// inspecting that expression's type with `ty.references_error()` will return
 138     /// true. Likewise, if an expression is known to diverge, inspecting its
 139     /// type with `ty::type_is_bot` will return true (n.b.: since Rust is
 140     /// strict, _|_ can appear in the type of an expression that does not,
 141     /// itself, diverge: for example, fn() -> _|_.)
 142     /// Note that inspecting a type's structure *directly* may expose the fact
 143     /// that there are actually multiple representations for `Error`, so avoid
 144     /// that when err needs to be handled differently.
 145     fn check_expr_with_expectation_and_needs(
 146         &self,
 147         expr: &'tcx hir::Expr,
 148         expected: Expectation<'tcx>,
 149         needs: Needs,
 150     ) -> Ty<'tcx> {
 151         debug!(">> type-checking: expr={:?} expected={:?}",
 152                expr, expected);
 153
 154         // True if `expr` is a `Try::from_ok(())` that is a result of desugaring a try block
 155         // without the final expr (e.g. `try { return; }`). We don't want to generate an
 156         // unreachable_code lint for it since warnings for autogenerated code are confusing.
 157         let is_try_block_generated_unit_expr = match expr.kind {
 158             ExprKind::Call(_, ref args) if expr.span.is_desugaring(DesugaringKind::TryBlock) =>
 159                 args.len() == 1 && args[0].span.is_desugaring(DesugaringKind::TryBlock),
 160
 161             _ => false,
 162         };
 163
 164         // Warn for expressions after diverging siblings.
 165         if !is_try_block_generated_unit_expr {
 166             self.warn_if_unreachable(expr.hir_id, expr.span, "expression");
 167         }
 168
 169         // Hide the outer diverging and has_errors flags.
 170         let old_diverges = self.diverges.get();
 171         let old_has_errors = self.has_errors.get();
 172         self.diverges.set(Diverges::Maybe);
 173         self.has_errors.set(false);
 174
 175         let ty = self.check_expr_kind(expr, expected, needs);
 176
 177         // Warn for non-block expressions with diverging children.
 178         match expr.kind {
 179             ExprKind::Block(..) | ExprKind::Loop(..) | ExprKind::Match(..) => {},
 180             // If `expr` is a result of desugaring the try block and is an ok-wrapped
 181             // diverging expression (e.g. it arose from desugaring of `try { return }`),
 182             // we skip issuing a warning because it is autogenerated code.
 183             ExprKind::Call(..) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {},
 184             ExprKind::Call(ref callee, _) =>
 185                 self.warn_if_unreachable(expr.hir_id, callee.span, "call"),
 186             ExprKind::MethodCall(_, ref span, _) =>
 187                 self.warn_if_unreachable(expr.hir_id, *span, "call"),
 188             _ => self.warn_if_unreachable(expr.hir_id, expr.span, "expression"),
 189         }
 190
 191         // Any expression that produces a value of type `!` must have diverged
 192         if ty.is_never() {
 193             self.diverges.set(self.diverges.get() | Diverges::always(expr.span));
 194         }
 195
 196         // Record the type, which applies it effects.
 197         // We need to do this after the warning above, so that
 198         // we don't warn for the diverging expression itself.
 199         self.write_ty(expr.hir_id, ty);
 200
 201         // Combine the diverging and has_error flags.
 202         self.diverges.set(self.diverges.get() | old_diverges);
 203         self.has_errors.set(self.has_errors.get() | old_has_errors);
 204
 205         debug!("type of {} is...", self.tcx.hir().node_to_string(expr.hir_id));
 206         debug!("... {:?}, expected is {:?}", ty, expected);
 207
 208         ty
 209     }
 210
 211     fn check_expr_kind(
 212         &self,
 213         expr: &'tcx hir::Expr,
 214         expected: Expectation<'tcx>,
 215         needs: Needs,
 216     ) -> Ty<'tcx> {
 217         debug!(
 218             "check_expr_kind(expr={:?}, expected={:?}, needs={:?})",
 219             expr,
 220             expected,
 221             needs,
 222         );
 223
 224         let tcx = self.tcx;
 225         match expr.kind {
 226             ExprKind::Box(ref subexpr) => {
 227                 self.check_expr_box(subexpr, expected)
 228             }
 229             ExprKind::Lit(ref lit) => {
 230                 self.check_lit(&lit, expected)
 231             }
 232             ExprKind::Binary(op, ref lhs, ref rhs) => {
 233                 self.check_binop(expr, op, lhs, rhs)
 234             }
 235             ExprKind::AssignOp(op, ref lhs, ref rhs) => {
 236                 self.check_binop_assign(expr, op, lhs, rhs)
 237             }
 238             ExprKind::Unary(unop, ref oprnd) => {
 239                 self.check_expr_unary(unop, oprnd, expected, needs, expr)
 240             }
 241             ExprKind::AddrOf(kind, mutbl, ref oprnd) => {
 242                 self.check_expr_addr_of(kind, mutbl, oprnd, expected, expr)
 243             }
 244             ExprKind::Path(ref qpath) => {
 245                 self.check_expr_path(qpath, expr)
 246             }
 247             ExprKind::InlineAsm(ref asm) => {
 248                 for expr in asm.outputs_exprs.iter().chain(asm.inputs_exprs.iter()) {
 249                     self.check_expr(expr);
 250                 }
 251                 tcx.mk_unit()
 252             }
 253             ExprKind::Break(destination, ref expr_opt) => {
 254                 self.check_expr_break(destination, expr_opt.as_deref(), expr)
 255             }
 256             ExprKind::Continue(destination) => {
 257                 if destination.target_id.is_ok() {
 258                     tcx.types.never
 259                 } else {
 260                     // There was an error; make type-check fail.
 261                     tcx.types.err
 262                 }
 263             }
 264             ExprKind::Ret(ref expr_opt) => {
 265                 self.check_expr_return(expr_opt.as_deref(), expr)
 266             }
 267             ExprKind::Assign(ref lhs, ref rhs) => {
 268                 self.check_expr_assign(expr, expected, lhs, rhs)
 269             }
 270             ExprKind::Loop(ref body, _, source) => {
 271                 self.check_expr_loop(body, source, expected, expr)
 272             }
 273             ExprKind::Match(ref discrim, ref arms, match_src) => {
 274                 self.check_match(expr, &discrim, arms, expected, match_src)
 275             }
 276             ExprKind::Closure(capture, ref decl, body_id, _, gen) => {
 277                 self.check_expr_closure(expr, capture, &decl, body_id, gen, expected)
 278             }
 279             ExprKind::Block(ref body, _) => {
 280                 self.check_block_with_expected(&body, expected)
 281             }
 282             ExprKind::Call(ref callee, ref args) => {
 283                 self.check_call(expr, &callee, args, expected)
 284             }
 285             ExprKind::MethodCall(ref segment, span, ref args) => {
 286                 self.check_method_call(expr, segment, span, args, expected, needs)
 287             }
 288             ExprKind::Cast(ref e, ref t) => {
 289                 self.check_expr_cast(e, t, expr)
 290             }
 291             ExprKind::Type(ref e, ref t) => {
 292                 let ty = self.to_ty_saving_user_provided_ty(&t);
 293                 self.check_expr_eq_type(&e, ty);
 294                 ty
 295             }
 296             ExprKind::DropTemps(ref e) => {
 297                 self.check_expr_with_expectation(e, expected)
 298             }
 299             ExprKind::Array(ref args) => {
 300                 self.check_expr_array(args, expected, expr)
 301             }
 302             ExprKind::Repeat(ref element, ref count) => {
 303                 self.check_expr_repeat(element, count, expected, expr)
 304             }
 305             ExprKind::Tup(ref elts) => {
 306                 self.check_expr_tuple(elts, expected, expr)
 307             }
 308             ExprKind::Struct(ref qpath, ref fields, ref base_expr) => {
 309                 self.check_expr_struct(expr, expected, qpath, fields, base_expr)
 310             }
 311             ExprKind::Field(ref base, field) => {
 312                 self.check_field(expr, needs, &base, field)
 313             }
 314             ExprKind::Index(ref base, ref idx) => {
 315                 self.check_expr_index(base, idx, needs, expr)
 316             }
 317             ExprKind::Yield(ref value, ref src) => {
 318                 self.check_expr_yield(value, expr, src)
 319             }
 320             hir::ExprKind::Err => {
 321                 tcx.types.err
 322             }
 323         }
 324     }
 325
 326     fn check_expr_box(&self, expr: &'tcx hir::Expr, expected: Expectation<'tcx>) -> Ty<'tcx> {
 327         let expected_inner = expected.to_option(self).map_or(NoExpectation, |ty| {
 328             match ty.kind {
 329                 ty::Adt(def, _) if def.is_box()
 330                     => Expectation::rvalue_hint(self, ty.boxed_ty()),
 331                 _ => NoExpectation
 332             }
 333         });
 334         let referent_ty = self.check_expr_with_expectation(expr, expected_inner);
 335         self.tcx.mk_box(referent_ty)
 336     }
 337
 338     fn check_expr_unary(
 339         &self,
 340         unop: hir::UnOp,
 341         oprnd: &'tcx hir::Expr,
 342         expected: Expectation<'tcx>,
 343         needs: Needs,
 344         expr: &'tcx hir::Expr,
 345     ) -> Ty<'tcx> {
 346         let tcx = self.tcx;
 347         let expected_inner = match unop {
 348             hir::UnNot | hir::UnNeg => expected,
 349             hir::UnDeref => NoExpectation,
 350         };
 351         let needs = match unop {
 352             hir::UnDeref => needs,
 353             _ => Needs::None
 354         };
 355         let mut oprnd_t = self.check_expr_with_expectation_and_needs(&oprnd, expected_inner, needs);
 356
 357         if !oprnd_t.references_error() {
 358             oprnd_t = self.structurally_resolved_type(expr.span, oprnd_t);
 359             match unop {
 360                 hir::UnDeref => {
 361                     if let Some(mt) = oprnd_t.builtin_deref(true) {
 362                         oprnd_t = mt.ty;
 363                     } else if let Some(ok) = self.try_overloaded_deref(
 364                             expr.span, oprnd_t, needs) {
 365                         let method = self.register_infer_ok_obligations(ok);
 366                         if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind {
 367                             let mutbl = match mutbl {
 368                                 hir::Mutability::Immutable => AutoBorrowMutability::Immutable,
 369                                 hir::Mutability::Mutable => AutoBorrowMutability::Mutable {
 370                                     // (It shouldn't actually matter for unary ops whether
 371                                     // we enable two-phase borrows or not, since a unary
 372                                     // op has no additional operands.)
 373                                     allow_two_phase_borrow: AllowTwoPhase::No,
 374                                 }
 375                             };
 376                             self.apply_adjustments(oprnd, vec![Adjustment {
 377                                 kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 378                                 target: method.sig.inputs()[0]
 379                             }]);
 380                         }
 381                         oprnd_t = self.make_overloaded_place_return_type(method).ty;
 382                         self.write_method_call(expr.hir_id, method);
 383                     } else {
 384                         let mut err = type_error_struct!(
 385                             tcx.sess,
 386                             expr.span,
 387                             oprnd_t,
 388                             E0614,
 389                             "type `{}` cannot be dereferenced",
 390                             oprnd_t,
 391                         );
 392                         let sp = tcx.sess.source_map().start_point(expr.span);
 393                         if let Some(sp) = tcx.sess.parse_sess.ambiguous_block_expr_parse
 394                             .borrow().get(&sp)
 395                         {
 396                             tcx.sess.parse_sess.expr_parentheses_needed(
 397                                 &mut err,
 398                                 *sp,
 399                                 None,
 400                             );
 401                         }
 402                         err.emit();
 403                         oprnd_t = tcx.types.err;
 404                     }
 405                 }
 406                 hir::UnNot => {
 407                     let result = self.check_user_unop(expr, oprnd_t, unop);
 408                     // If it's builtin, we can reuse the type, this helps inference.
 409                     if !(oprnd_t.is_integral() || oprnd_t.kind == ty::Bool) {
 410                         oprnd_t = result;
 411                     }
 412                 }
 413                 hir::UnNeg => {
 414                     let result = self.check_user_unop(expr, oprnd_t, unop);
 415                     // If it's builtin, we can reuse the type, this helps inference.
 416                     if !oprnd_t.is_numeric() {
 417                         oprnd_t = result;
 418                     }
 419                 }
 420             }
 421         }
 422         oprnd_t
 423     }
 424
 425     fn check_expr_addr_of(
 426         &self,
 427         kind: hir::BorrowKind,
 428         mutbl: hir::Mutability,
 429         oprnd: &'tcx hir::Expr,
 430         expected: Expectation<'tcx>,
 431         expr: &'tcx hir::Expr,
 432     ) -> Ty<'tcx> {
 433         let hint = expected.only_has_type(self).map_or(NoExpectation, |ty| {
 434             match ty.kind {
 435                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 436                     if oprnd.is_syntactic_place_expr() {
 437                         // Places may legitimately have unsized types.
 438                         // For example, dereferences of a fat pointer and
 439                         // the last field of a struct can be unsized.
 440                         ExpectHasType(ty)
 441                     } else {
 442                         Expectation::rvalue_hint(self, ty)
 443                     }
 444                 }
 445                 _ => NoExpectation
 446             }
 447         });
 448         let needs = Needs::maybe_mut_place(mutbl);
 449         let ty = self.check_expr_with_expectation_and_needs(&oprnd, hint, needs);
 450
 451         let tm = ty::TypeAndMut { ty: ty, mutbl: mutbl };
 452         match kind {
 453             _ if tm.ty.references_error() => self.tcx.types.err,
 454             hir::BorrowKind::Raw => {
 455                 self.check_named_place_expr(oprnd);
 456                 self.tcx.mk_ptr(tm)
 457             }
 458             hir::BorrowKind::Ref => {
 459                 // Note: at this point, we cannot say what the best lifetime
 460                 // is to use for resulting pointer.  We want to use the
 461                 // shortest lifetime possible so as to avoid spurious borrowck
 462                 // errors.  Moreover, the longest lifetime will depend on the
 463                 // precise details of the value whose address is being taken
 464                 // (and how long it is valid), which we don't know yet until
 465                 // type inference is complete.
 466                 //
 467                 // Therefore, here we simply generate a region variable. The
 468                 // region inferencer will then select a suitable value.
 469                 // Finally, borrowck will infer the value of the region again,
 470                 // this time with enough precision to check that the value
 471                 // whose address was taken can actually be made to live as long
 472                 // as it needs to live.
 473                 let region = self.next_region_var(infer::AddrOfRegion(expr.span));
 474                 self.tcx.mk_ref(region, tm)
 475             }
 476         }
 477     }
 478
 479     /// Does this expression refer to a place that either:
 480     /// * Is based on a local or static.
 481     /// * Contains a dereference
 482     /// Note that the adjustments for the children of `expr` should already
 483     /// have been resolved.
 484     fn check_named_place_expr(&self, oprnd: &'tcx hir::Expr) {
 485         let is_named = oprnd.is_place_expr(|base| {
 486             // Allow raw borrows if there are any deref adjustments.
 487             //
 488             // const VAL: (i32,) = (0,);
 489             // const REF: &(i32,) = &(0,);
 490             //
 491             // &raw const VAL.0;            // ERROR
 492             // &raw const REF.0;            // OK, same as &raw const (*REF).0;
 493             //
 494             // This is maybe too permissive, since it allows
 495             // `let u = &raw const Box::new((1,)).0`, which creates an
 496             // immediately dangling raw pointer.
 497             self.tables.borrow().adjustments().get(base.hir_id).map_or(false, |x| {
 498                 x.iter().any(|adj| if let Adjust::Deref(_) = adj.kind {
 499                     true
 500                 } else {
 501                     false
 502                 })
 503             })
 504         });
 505         if !is_named {
 506             struct_span_err!(self.tcx.sess, oprnd.span, E0745, "cannot take address of a temporary")
 507                 .span_label(oprnd.span, "temporary value")
 508                 .emit();
 509         }
 510     }
 511
 512     fn check_expr_path(&self, qpath: &hir::QPath, expr: &'tcx hir::Expr) -> Ty<'tcx> {
 513         let tcx = self.tcx;
 514         let (res, opt_ty, segs) = self.resolve_ty_and_res_ufcs(qpath, expr.hir_id, expr.span);
 515         let ty = match res {
 516             Res::Err => {
 517                 self.set_tainted_by_errors();
 518                 tcx.types.err
 519             }
 520             Res::Def(DefKind::Ctor(_, CtorKind::Fictive), _) => {
 521                 report_unexpected_variant_res(tcx, res, expr.span, qpath);
 522                 tcx.types.err
 523             }
 524             _ => self.instantiate_value_path(segs, opt_ty, res, expr.span, expr.hir_id).0,
 525         };
 526
 527         if let ty::FnDef(..) = ty.kind {
 528             let fn_sig = ty.fn_sig(tcx);
 529             if !tcx.features().unsized_locals {
 530                 // We want to remove some Sized bounds from std functions,
 531                 // but don't want to expose the removal to stable Rust.
 532                 // i.e., we don't want to allow
 533                 //
 534                 // ```rust
 535                 // drop as fn(str);
 536                 // ```
 537                 //
 538                 // to work in stable even if the Sized bound on `drop` is relaxed.
 539                 for i in 0..fn_sig.inputs().skip_binder().len() {
 540                     // We just want to check sizedness, so instead of introducing
 541                     // placeholder lifetimes with probing, we just replace higher lifetimes
 542                     // with fresh vars.
 543                     let input = self.replace_bound_vars_with_fresh_vars(
 544                         expr.span,
 545                         infer::LateBoundRegionConversionTime::FnCall,
 546                         &fn_sig.input(i)).0;
 547                     self.require_type_is_sized_deferred(input, expr.span,
 548                                                         traits::SizedArgumentType);
 549                 }
 550             }
 551             // Here we want to prevent struct constructors from returning unsized types.
 552             // There were two cases this happened: fn pointer coercion in stable
 553             // and usual function call in presence of unsized_locals.
 554             // Also, as we just want to check sizedness, instead of introducing
 555             // placeholder lifetimes with probing, we just replace higher lifetimes
 556             // with fresh vars.
 557             let output = self.replace_bound_vars_with_fresh_vars(
 558                 expr.span,
 559                 infer::LateBoundRegionConversionTime::FnCall,
 560                 &fn_sig.output()).0;
 561             self.require_type_is_sized_deferred(output, expr.span, traits::SizedReturnType);
 562         }
 563
 564         // We always require that the type provided as the value for
 565         // a type parameter outlives the moment of instantiation.
 566         let substs = self.tables.borrow().node_substs(expr.hir_id);
 567         self.add_wf_bounds(substs, expr);
 568
 569         ty
 570     }
 571
 572     fn check_expr_break(
 573         &self,
 574         destination: hir::Destination,
 575         expr_opt: Option<&'tcx hir::Expr>,
 576         expr: &'tcx hir::Expr,
 577     ) -> Ty<'tcx> {
 578         let tcx = self.tcx;
 579         if let Ok(target_id) = destination.target_id {
 580             let (e_ty, cause);
 581             if let Some(ref e) = expr_opt {
 582                 // If this is a break with a value, we need to type-check
 583                 // the expression. Get an expected type from the loop context.
 584                 let opt_coerce_to = {
 585                     // We should release `enclosing_breakables` before the `check_expr_with_hint`
 586                     // below, so can't move this block of code to the enclosing scope and share
 587                     // `ctxt` with the second `encloding_breakables` borrow below.
 588                     let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 589                     match enclosing_breakables.opt_find_breakable(target_id) {
 590                         Some(ctxt) =>
 591                             ctxt.coerce.as_ref().map(|coerce| coerce.expected_ty()),
 592                         None => { // Avoid ICE when `break` is inside a closure (#65383).
 593                             self.tcx.sess.delay_span_bug(
 594                                 expr.span,
 595                                 "break was outside loop, but no error was emitted",
 596                             );
 597                             return tcx.types.err;
 598                         }
 599                     }
 600                 };
 601
 602                 // If the loop context is not a `loop { }`, then break with
 603                 // a value is illegal, and `opt_coerce_to` will be `None`.
 604                 // Just set expectation to error in that case.
 605                 let coerce_to = opt_coerce_to.unwrap_or(tcx.types.err);
 606
 607                 // Recurse without `enclosing_breakables` borrowed.
 608                 e_ty = self.check_expr_with_hint(e, coerce_to);
 609                 cause = self.misc(e.span);
 610             } else {
 611                 // Otherwise, this is a break *without* a value. That's
 612                 // always legal, and is equivalent to `break ()`.
 613                 e_ty = tcx.mk_unit();
 614                 cause = self.misc(expr.span);
 615             }
 616
 617             // Now that we have type-checked `expr_opt`, borrow
 618             // the `enclosing_loops` field and let's coerce the
 619             // type of `expr_opt` into what is expected.
 620             let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 621             let ctxt = match enclosing_breakables.opt_find_breakable(target_id) {
 622                 Some(ctxt) => ctxt,
 623                 None => { // Avoid ICE when `break` is inside a closure (#65383).
 624                     self.tcx.sess.delay_span_bug(
 625                         expr.span,
 626                         "break was outside loop, but no error was emitted",
 627                     );
 628                     return tcx.types.err;
 629                 }
 630             };
 631
 632             if let Some(ref mut coerce) = ctxt.coerce {
 633                 if let Some(ref e) = expr_opt {
 634                     coerce.coerce(self, &cause, e, e_ty);
 635                 } else {
 636                     assert!(e_ty.is_unit());
 637                     let ty = coerce.expected_ty();
 638                     coerce.coerce_forced_unit(self, &cause, &mut |mut err| {
 639                         self.suggest_mismatched_types_on_tail(
 640                             &mut err,
 641                             expr,
 642                             ty,
 643                             e_ty,
 644                             cause.span,
 645                             target_id,
 646                         );
 647                         if let Some(val) = ty_kind_suggestion(ty) {
 648                             let label = destination.label
 649                                 .map(|l| format!(" {}", l.ident))
 650                                 .unwrap_or_else(String::new);
 651                             err.span_suggestion(
 652                                 expr.span,
 653                                 "give it a value of the expected type",
 654                                 format!("break{} {}", label, val),
 655                                 Applicability::HasPlaceholders,
 656                             );
 657                         }
 658                     }, false);
 659                 }
 660             } else {
 661                 // If `ctxt.coerce` is `None`, we can just ignore
 662                 // the type of the expression.  This is because
 663                 // either this was a break *without* a value, in
 664                 // which case it is always a legal type (`()`), or
 665                 // else an error would have been flagged by the
 666                 // `loops` pass for using break with an expression
 667                 // where you are not supposed to.
 668                 assert!(expr_opt.is_none() || self.tcx.sess.has_errors());
 669             }
 670
 671             ctxt.may_break = true;
 672
 673             // the type of a `break` is always `!`, since it diverges
 674             tcx.types.never
 675         } else {
 676             // Otherwise, we failed to find the enclosing loop;
 677             // this can only happen if the `break` was not
 678             // inside a loop at all, which is caught by the
 679             // loop-checking pass.
 680             self.tcx.sess.delay_span_bug(expr.span,
 681                 "break was outside loop, but no error was emitted");
 682
 683             // We still need to assign a type to the inner expression to
 684             // prevent the ICE in #43162.
 685             if let Some(ref e) = expr_opt {
 686                 self.check_expr_with_hint(e, tcx.types.err);
 687
 688                 // ... except when we try to 'break rust;'.
 689                 // ICE this expression in particular (see #43162).
 690                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
 691                     if path.segments.len() == 1 &&
 692                         path.segments[0].ident.name == sym::rust {
 693                         fatally_break_rust(self.tcx.sess);
 694                     }
 695                 }
 696             }
 697             // There was an error; make type-check fail.
 698             tcx.types.err
 699         }
 700     }
 701
 702     fn check_expr_return(
 703         &self,
 704         expr_opt: Option<&'tcx hir::Expr>,
 705         expr: &'tcx hir::Expr
 706     ) -> Ty<'tcx> {
 707         if self.ret_coercion.is_none() {
 708             struct_span_err!(
 709                 self.tcx.sess,
 710                 expr.span,
 711                 E0572,
 712                 "return statement outside of function body",
 713             ).emit();
 714         } else if let Some(ref e) = expr_opt {
 715             if self.ret_coercion_span.borrow().is_none() {
 716                 *self.ret_coercion_span.borrow_mut() = Some(e.span);
 717             }
 718             self.check_return_expr(e);
 719         } else {
 720             let mut coercion = self.ret_coercion.as_ref().unwrap().borrow_mut();
 721             if self.ret_coercion_span.borrow().is_none() {
 722                 *self.ret_coercion_span.borrow_mut() = Some(expr.span);
 723             }
 724             let cause = self.cause(expr.span, ObligationCauseCode::ReturnNoExpression);
 725             if let Some((fn_decl, _)) = self.get_fn_decl(expr.hir_id) {
 726                 coercion.coerce_forced_unit(
 727                     self,
 728                     &cause,
 729                     &mut |db| {
 730                         db.span_label(
 731                             fn_decl.output.span(),
 732                             format!(
 733                                 "expected `{}` because of this return type",
 734                                 fn_decl.output,
 735                             ),
 736                         );
 737                     },
 738                     true,
 739                 );
 740             } else {
 741                 coercion.coerce_forced_unit(self, &cause, &mut |_| (), true);
 742             }
 743         }
 744         self.tcx.types.never
 745     }
 746
 747     pub(super) fn check_return_expr(&self, return_expr: &'tcx hir::Expr) {
 748         let ret_coercion =
 749             self.ret_coercion
 750                 .as_ref()
 751                 .unwrap_or_else(|| span_bug!(return_expr.span,
 752                                              "check_return_expr called outside fn body"));
 753
 754         let ret_ty = ret_coercion.borrow().expected_ty();
 755         let return_expr_ty = self.check_expr_with_hint(return_expr, ret_ty.clone());
 756         ret_coercion.borrow_mut().coerce(
 757             self,
 758             &self.cause(return_expr.span, ObligationCauseCode::ReturnValue(return_expr.hir_id)),
 759             return_expr,
 760             return_expr_ty,
 761         );
 762     }
 763
 764     /// Type check assignment expression `expr` of form `lhs = rhs`.
 765     /// The expected type is `()` and is passsed to the function for the purposes of diagnostics.
 766     fn check_expr_assign(
 767         &self,
 768         expr: &'tcx hir::Expr,
 769         expected: Expectation<'tcx>,
 770         lhs: &'tcx hir::Expr,
 771         rhs: &'tcx hir::Expr,
 772     ) -> Ty<'tcx> {
 773         let lhs_ty = self.check_expr_with_needs(&lhs, Needs::MutPlace);
 774         let rhs_ty = self.check_expr_coercable_to_type(&rhs, lhs_ty);
 775
 776         let expected_ty = expected.coercion_target_type(self, expr.span);
 777         if expected_ty == self.tcx.types.bool {
 778             // The expected type is `bool` but this will result in `()` so we can reasonably
 779             // say that the user intended to write `lhs == rhs` instead of `lhs = rhs`.
 780             // The likely cause of this is `if foo = bar { .. }`.
 781             let actual_ty = self.tcx.mk_unit();
 782             let mut err = self.demand_suptype_diag(expr.span, expected_ty, actual_ty).unwrap();
 783             let msg = "try comparing for equality";
 784             let left = self.tcx.sess.source_map().span_to_snippet(lhs.span);
 785             let right = self.tcx.sess.source_map().span_to_snippet(rhs.span);
 786             if let (Ok(left), Ok(right)) = (left, right) {
 787                 let help = format!("{} == {}", left, right);
 788                 err.span_suggestion(expr.span, msg, help, Applicability::MaybeIncorrect);
 789             } else {
 790                 err.help(msg);
 791             }
 792             err.emit();
 793         } else if !lhs.is_syntactic_place_expr() {
 794             struct_span_err!(self.tcx.sess, expr.span, E0070,
 795                                 "invalid left-hand side expression")
 796                 .span_label(expr.span, "left-hand of expression not valid")
 797                 .emit();
 798         }
 799
 800         self.require_type_is_sized(lhs_ty, lhs.span, traits::AssignmentLhsSized);
 801
 802         if lhs_ty.references_error() || rhs_ty.references_error() {
 803             self.tcx.types.err
 804         } else {
 805             self.tcx.mk_unit()
 806         }
 807     }
 808
 809     fn check_expr_loop(
 810         &self,
 811         body: &'tcx hir::Block,
 812         source: hir::LoopSource,
 813         expected: Expectation<'tcx>,
 814         expr: &'tcx hir::Expr,
 815     ) -> Ty<'tcx> {
 816         let coerce = match source {
 817             // you can only use break with a value from a normal `loop { }`
 818             hir::LoopSource::Loop => {
 819                 let coerce_to = expected.coercion_target_type(self, body.span);
 820                 Some(CoerceMany::new(coerce_to))
 821             }
 822
 823             hir::LoopSource::While |
 824             hir::LoopSource::WhileLet |
 825             hir::LoopSource::ForLoop => {
 826                 None
 827             }
 828         };
 829
 830         let ctxt = BreakableCtxt {
 831             coerce,
 832             may_break: false, // Will get updated if/when we find a `break`.
 833         };
 834
 835         let (ctxt, ()) = self.with_breakable_ctxt(expr.hir_id, ctxt, || {
 836             self.check_block_no_value(&body);
 837         });
 838
 839         if ctxt.may_break {
 840             // No way to know whether it's diverging because
 841             // of a `break` or an outer `break` or `return`.
 842             self.diverges.set(Diverges::Maybe);
 843         }
 844
 845         // If we permit break with a value, then result type is
 846         // the LUB of the breaks (possibly ! if none); else, it
 847         // is nil. This makes sense because infinite loops
 848         // (which would have type !) are only possible iff we
 849         // permit break with a value [1].
 850         if ctxt.coerce.is_none() && !ctxt.may_break {
 851             // [1]
 852             self.tcx.sess.delay_span_bug(body.span, "no coercion, but loop may not break");
 853         }
 854         ctxt.coerce.map(|c| c.complete(self)).unwrap_or_else(|| self.tcx.mk_unit())
 855     }
 856
 857     /// Checks a method call.
 858     fn check_method_call(
 859         &self,
 860         expr: &'tcx hir::Expr,
 861         segment: &hir::PathSegment,
 862         span: Span,
 863         args: &'tcx [hir::Expr],
 864         expected: Expectation<'tcx>,
 865         needs: Needs,
 866     ) -> Ty<'tcx> {
 867         let rcvr = &args[0];
 868         let rcvr_t = self.check_expr_with_needs(&rcvr, needs);
 869         // no need to check for bot/err -- callee does that
 870         let rcvr_t = self.structurally_resolved_type(args[0].span, rcvr_t);
 871
 872         let method = match self.lookup_method(rcvr_t, segment, span, expr, rcvr) {
 873             Ok(method) => {
 874                 self.write_method_call(expr.hir_id, method);
 875                 Ok(method)
 876             }
 877             Err(error) => {
 878                 if segment.ident.name != kw::Invalid {
 879                     self.report_extended_method_error(segment, span, args, rcvr_t, error);
 880                 }
 881                 Err(())
 882             }
 883         };
 884
 885         // Call the generic checker.
 886         self.check_method_argument_types(
 887             span,
 888             expr,
 889             method,
 890             &args[1..],
 891             DontTupleArguments,
 892             expected,
 893         )
 894     }
 895
 896     fn report_extended_method_error(
 897         &self,
 898         segment: &hir::PathSegment,
 899         span: Span,
 900         args: &'tcx [hir::Expr],
 901         rcvr_t: Ty<'tcx>,
 902         error: MethodError<'tcx>
 903     ) {
 904         let rcvr = &args[0];
 905         let try_alt_rcvr = |err: &mut DiagnosticBuilder<'_>, rcvr_t, lang_item| {
 906             if let Some(new_rcvr_t) = self.tcx.mk_lang_item(rcvr_t, lang_item) {
 907                 if let Ok(pick) = self.lookup_probe(
 908                     span,
 909                     segment.ident,
 910                     new_rcvr_t,
 911                     rcvr,
 912                     probe::ProbeScope::AllTraits,
 913                 ) {
 914                     err.span_label(
 915                         pick.item.ident.span,
 916                         &format!("the method is available for `{}` here", new_rcvr_t),
 917                     );
 918                 }
 919             }
 920         };
 921
 922         if let Some(mut err) = self.report_method_error(
 923             span,
 924             rcvr_t,
 925             segment.ident,
 926             SelfSource::MethodCall(rcvr),
 927             error,
 928             Some(args),
 929         ) {
 930             if let ty::Adt(..) = rcvr_t.kind {
 931                 // Try alternative arbitrary self types that could fulfill this call.
 932                 // FIXME: probe for all types that *could* be arbitrary self-types, not
 933                 // just this whitelist.
 934                 try_alt_rcvr(&mut err, rcvr_t, lang_items::OwnedBoxLangItem);
 935                 try_alt_rcvr(&mut err, rcvr_t, lang_items::PinTypeLangItem);
 936                 try_alt_rcvr(&mut err, rcvr_t, lang_items::Arc);
 937                 try_alt_rcvr(&mut err, rcvr_t, lang_items::Rc);
 938             }
 939             err.emit();
 940         }
 941     }
 942
 943     fn check_expr_cast(
 944         &self,
 945         e: &'tcx hir::Expr,
 946         t: &'tcx hir::Ty,
 947         expr: &'tcx hir::Expr,
 948     ) -> Ty<'tcx> {
 949         // Find the type of `e`. Supply hints based on the type we are casting to,
 950         // if appropriate.
 951         let t_cast = self.to_ty_saving_user_provided_ty(t);
 952         let t_cast = self.resolve_vars_if_possible(&t_cast);
 953         let t_expr = self.check_expr_with_expectation(e, ExpectCastableToType(t_cast));
 954         let t_cast = self.resolve_vars_if_possible(&t_cast);
 955
 956         // Eagerly check for some obvious errors.
 957         if t_expr.references_error() || t_cast.references_error() {
 958             self.tcx.types.err
 959         } else {
 960             // Defer other checks until we're done type checking.
 961             let mut deferred_cast_checks = self.deferred_cast_checks.borrow_mut();
 962             match cast::CastCheck::new(self, e, t_expr, t_cast, t.span, expr.span) {
 963                 Ok(cast_check) => {
 964                     deferred_cast_checks.push(cast_check);
 965                     t_cast
 966                 }
 967                 Err(ErrorReported) => {
 968                     self.tcx.types.err
 969                 }
 970             }
 971         }
 972     }
 973
 974     fn check_expr_array(
 975         &self,
 976         args: &'tcx [hir::Expr],
 977         expected: Expectation<'tcx>,
 978         expr: &'tcx hir::Expr
 979     ) -> Ty<'tcx> {
 980         let uty = expected.to_option(self).and_then(|uty| {
 981             match uty.kind {
 982                 ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
 983                 _ => None
 984             }
 985         });
 986
 987         let element_ty = if !args.is_empty() {
 988             let coerce_to = uty.unwrap_or_else(|| {
 989                 self.next_ty_var(TypeVariableOrigin {
 990                     kind: TypeVariableOriginKind::TypeInference,
 991                     span: expr.span,
 992                 })
 993             });
 994             let mut coerce = CoerceMany::with_coercion_sites(coerce_to, args);
 995             assert_eq!(self.diverges.get(), Diverges::Maybe);
 996             for e in args {
 997                 let e_ty = self.check_expr_with_hint(e, coerce_to);
 998                 let cause = self.misc(e.span);
 999                 coerce.coerce(self, &cause, e, e_ty);
1000             }
1001             coerce.complete(self)
1002         } else {
1003             self.next_ty_var(TypeVariableOrigin {
1004                 kind: TypeVariableOriginKind::TypeInference,
1005                 span: expr.span,
1006             })
1007         };
1008         self.tcx.mk_array(element_ty, args.len() as u64)
1009     }
1010
1011     fn check_expr_repeat(
1012         &self,
1013         element: &'tcx hir::Expr,
1014         count: &'tcx hir::AnonConst,
1015         expected: Expectation<'tcx>,
1016         _expr: &'tcx hir::Expr,
1017     ) -> Ty<'tcx> {
1018         let tcx = self.tcx;
1019         let count_def_id = tcx.hir().local_def_id(count.hir_id);
1020         let count = if self.const_param_def_id(count).is_some() {
1021             Ok(self.to_const(count, tcx.type_of(count_def_id)))
1022         } else {
1023             let param_env = ty::ParamEnv::empty();
1024             let substs = InternalSubsts::identity_for_item(tcx, count_def_id);
1025             let instance = ty::Instance::resolve(
1026                 tcx,
1027                 param_env,
1028                 count_def_id,
1029                 substs,
1030             ).unwrap();
1031             let global_id = GlobalId {
1032                 instance,
1033                 promoted: None
1034             };
1035
1036             tcx.const_eval(param_env.and(global_id))
1037         };
1038
1039         let uty = match expected {
1040             ExpectHasType(uty) => {
1041                 match uty.kind {
1042                     ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
1043                     _ => None
1044                 }
1045             }
1046             _ => None
1047         };
1048
1049         let (element_ty, t) = match uty {
1050             Some(uty) => {
1051                 self.check_expr_coercable_to_type(&element, uty);
1052                 (uty, uty)
1053             }
1054             None => {
1055                 let ty = self.next_ty_var(TypeVariableOrigin {
1056                     kind: TypeVariableOriginKind::MiscVariable,
1057                     span: element.span,
1058                 });
1059                 let element_ty = self.check_expr_has_type_or_error(&element, ty, |_| {});
1060                 (element_ty, ty)
1061             }
1062         };
1063
1064         if element_ty.references_error() {
1065             tcx.types.err
1066         } else if let Ok(count) = count {
1067             tcx.mk_ty(ty::Array(t, count))
1068         } else {
1069             tcx.types.err
1070         }
1071     }
1072
1073     fn check_expr_tuple(
1074         &self,
1075         elts: &'tcx [hir::Expr],
1076         expected: Expectation<'tcx>,
1077         expr: &'tcx hir::Expr,
1078     ) -> Ty<'tcx> {
1079         let flds = expected.only_has_type(self).and_then(|ty| {
1080             let ty = self.resolve_vars_with_obligations(ty);
1081             match ty.kind {
1082                 ty::Tuple(ref flds) => Some(&flds[..]),
1083                 _ => None
1084             }
1085         });
1086
1087         let elt_ts_iter = elts.iter().enumerate().map(|(i, e)| {
1088             let t = match flds {
1089                 Some(ref fs) if i < fs.len() => {
1090                     let ety = fs[i].expect_ty();
1091                     self.check_expr_coercable_to_type(&e, ety);
1092                     ety
1093                 }
1094                 _ => {
1095                     self.check_expr_with_expectation(&e, NoExpectation)
1096                 }
1097             };
1098             t
1099         });
1100         let tuple = self.tcx.mk_tup(elt_ts_iter);
1101         if tuple.references_error() {
1102             self.tcx.types.err
1103         } else {
1104             self.require_type_is_sized(tuple, expr.span, traits::TupleInitializerSized);
1105             tuple
1106         }
1107     }
1108
1109     fn check_expr_struct(
1110         &self,
1111         expr: &hir::Expr,
1112         expected: Expectation<'tcx>,
1113         qpath: &QPath,
1114         fields: &'tcx [hir::Field],
1115         base_expr: &'tcx Option<P<hir::Expr>>,
1116     ) -> Ty<'tcx> {
1117         // Find the relevant variant
1118         let (variant, adt_ty) =
1119             if let Some(variant_ty) = self.check_struct_path(qpath, expr.hir_id) {
1120                 variant_ty
1121             } else {
1122                 self.check_struct_fields_on_error(fields, base_expr);
1123                 return self.tcx.types.err;
1124             };
1125
1126         let path_span = match *qpath {
1127             QPath::Resolved(_, ref path) => path.span,
1128             QPath::TypeRelative(ref qself, _) => qself.span
1129         };
1130
1131         // Prohibit struct expressions when non-exhaustive flag is set.
1132         let adt = adt_ty.ty_adt_def().expect("`check_struct_path` returned non-ADT type");
1133         if !adt.did.is_local() && variant.is_field_list_non_exhaustive() {
1134             span_err!(self.tcx.sess, expr.span, E0639,
1135                       "cannot create non-exhaustive {} using struct expression",
1136                       adt.variant_descr());
1137         }
1138
1139         let error_happened = self.check_expr_struct_fields(adt_ty, expected, expr.hir_id, path_span,
1140                                                            variant, fields, base_expr.is_none());
1141         if let &Some(ref base_expr) = base_expr {
1142             // If check_expr_struct_fields hit an error, do not attempt to populate
1143             // the fields with the base_expr. This could cause us to hit errors later
1144             // when certain fields are assumed to exist that in fact do not.
1145             if !error_happened {
1146                 self.check_expr_has_type_or_error(base_expr, adt_ty, |_| {});
1147                 match adt_ty.kind {
1148                     ty::Adt(adt, substs) if adt.is_struct() => {
1149                         let fru_field_types = adt.non_enum_variant().fields.iter().map(|f| {
1150                             self.normalize_associated_types_in(expr.span, &f.ty(self.tcx, substs))
1151                         }).collect();
1152
1153                         self.tables
1154                             .borrow_mut()
1155                             .fru_field_types_mut()
1156                             .insert(expr.hir_id, fru_field_types);
1157                     }
1158                     _ => {
1159                         span_err!(self.tcx.sess, base_expr.span, E0436,
1160                                   "functional record update syntax requires a struct");
1161                     }
1162                 }
1163             }
1164         }
1165         self.require_type_is_sized(adt_ty, expr.span, traits::StructInitializerSized);
1166         adt_ty
1167     }
1168
1169     fn check_expr_struct_fields(
1170         &self,
1171         adt_ty: Ty<'tcx>,
1172         expected: Expectation<'tcx>,
1173         expr_id: hir::HirId,
1174         span: Span,
1175         variant: &'tcx ty::VariantDef,
1176         ast_fields: &'tcx [hir::Field],
1177         check_completeness: bool,
1178     ) -> bool {
1179         let tcx = self.tcx;
1180
1181         let adt_ty_hint =
1182             self.expected_inputs_for_expected_output(span, expected, adt_ty, &[adt_ty])
1183                 .get(0).cloned().unwrap_or(adt_ty);
1184         // re-link the regions that EIfEO can erase.
1185         self.demand_eqtype(span, adt_ty_hint, adt_ty);
1186
1187         let (substs, adt_kind, kind_name) = match &adt_ty.kind {
1188             &ty::Adt(adt, substs) => {
1189                 (substs, adt.adt_kind(), adt.variant_descr())
1190             }
1191             _ => span_bug!(span, "non-ADT passed to check_expr_struct_fields")
1192         };
1193
1194         let mut remaining_fields = variant.fields.iter().enumerate().map(|(i, field)|
1195             (field.ident.modern(), (i, field))
1196         ).collect::<FxHashMap<_, _>>();
1197
1198         let mut seen_fields = FxHashMap::default();
1199
1200         let mut error_happened = false;
1201
1202         // Type-check each field.
1203         for field in ast_fields {
1204             let ident = tcx.adjust_ident(field.ident, variant.def_id);
1205             let field_type = if let Some((i, v_field)) = remaining_fields.remove(&ident) {
1206                 seen_fields.insert(ident, field.span);
1207                 self.write_field_index(field.hir_id, i);
1208
1209                 // We don't look at stability attributes on
1210                 // struct-like enums (yet...), but it's definitely not
1211                 // a bug to have constructed one.
1212                 if adt_kind != AdtKind::Enum {
1213                     tcx.check_stability(v_field.did, Some(expr_id), field.span);
1214                 }
1215
1216                 self.field_ty(field.span, v_field, substs)
1217             } else {
1218                 error_happened = true;
1219                 if let Some(prev_span) = seen_fields.get(&ident) {
1220                     let mut err = struct_span_err!(self.tcx.sess,
1221                                                    field.ident.span,
1222                                                    E0062,
1223                                                    "field `{}` specified more than once",
1224                                                    ident);
1225
1226                     err.span_label(field.ident.span, "used more than once");
1227                     err.span_label(*prev_span, format!("first use of `{}`", ident));
1228
1229                     err.emit();
1230                 } else {
1231                     self.report_unknown_field(adt_ty, variant, field, ast_fields, kind_name, span);
1232                 }
1233
1234                 tcx.types.err
1235             };
1236
1237             // Make sure to give a type to the field even if there's
1238             // an error, so we can continue type-checking.
1239             self.check_expr_coercable_to_type(&field.expr, field_type);
1240         }
1241
1242         // Make sure the programmer specified correct number of fields.
1243         if kind_name == "union" {
1244             if ast_fields.len() != 1 {
1245                 tcx.sess.span_err(span, "union expressions should have exactly one field");
1246             }
1247         } else if check_completeness && !error_happened && !remaining_fields.is_empty() {
1248             let len = remaining_fields.len();
1249
1250             let mut displayable_field_names = remaining_fields
1251                                               .keys()
1252                                               .map(|ident| ident.as_str())
1253                                               .collect::<Vec<_>>();
1254
1255             displayable_field_names.sort();
1256
1257             let truncated_fields_error = if len <= 3 {
1258                 String::new()
1259             } else {
1260                 format!(" and {} other field{}", (len - 3), if len - 3 == 1 {""} else {"s"})
1261             };
1262
1263             let remaining_fields_names = displayable_field_names.iter().take(3)
1264                                         .map(|n| format!("`{}`", n))
1265                                         .collect::<Vec<_>>()
1266                                         .join(", ");
1267
1268             struct_span_err!(tcx.sess, span, E0063,
1269                              "missing field{} {}{} in initializer of `{}`",
1270                              pluralize!(remaining_fields.len()),
1271                              remaining_fields_names,
1272                              truncated_fields_error,
1273                              adt_ty)
1274                 .span_label(span, format!("missing {}{}",
1275                                           remaining_fields_names,
1276                                           truncated_fields_error))
1277                 .emit();
1278         }
1279         error_happened
1280     }
1281
1282     fn check_struct_fields_on_error(
1283         &self,
1284         fields: &'tcx [hir::Field],
1285         base_expr: &'tcx Option<P<hir::Expr>>,
1286     ) {
1287         for field in fields {
1288             self.check_expr(&field.expr);
1289         }
1290         if let Some(ref base) = *base_expr {
1291             self.check_expr(&base);
1292         }
1293     }
1294
1295     fn report_unknown_field(
1296         &self,
1297         ty: Ty<'tcx>,
1298         variant: &'tcx ty::VariantDef,
1299         field: &hir::Field,
1300         skip_fields: &[hir::Field],
1301         kind_name: &str,
1302         ty_span: Span
1303     ) {
1304         if variant.recovered {
1305             return;
1306         }
1307         let mut err = self.type_error_struct_with_diag(
1308             field.ident.span,
1309             |actual| match ty.kind {
1310                 ty::Adt(adt, ..) if adt.is_enum() => {
1311                     struct_span_err!(self.tcx.sess, field.ident.span, E0559,
1312                                      "{} `{}::{}` has no field named `{}`",
1313                                      kind_name, actual, variant.ident, field.ident)
1314                 }
1315                 _ => {
1316                     struct_span_err!(self.tcx.sess, field.ident.span, E0560,
1317                                      "{} `{}` has no field named `{}`",
1318                                      kind_name, actual, field.ident)
1319                 }
1320             },
1321             ty);
1322         match variant.ctor_kind {
1323             CtorKind::Fn => {
1324                 err.span_label(variant.ident.span, format!("`{adt}` defined here", adt=ty));
1325                 err.span_label(field.ident.span, "field does not exist");
1326                 err.span_label(ty_span, format!(
1327                         "`{adt}` is a tuple {kind_name}, \
1328                          use the appropriate syntax: `{adt}(/* fields */)`",
1329                     adt=ty,
1330                     kind_name=kind_name
1331                 ));
1332             }
1333             _ => {
1334                 // prevent all specified fields from being suggested
1335                 let skip_fields = skip_fields.iter().map(|ref x| x.ident.name);
1336                 if let Some(field_name) = Self::suggest_field_name(
1337                     variant,
1338                     &field.ident.as_str(),
1339                     skip_fields.collect()
1340                 ) {
1341                     err.span_suggestion(
1342                         field.ident.span,
1343                         "a field with a similar name exists",
1344                         field_name.to_string(),
1345                         Applicability::MaybeIncorrect,
1346                     );
1347                 } else {
1348                     match ty.kind {
1349                         ty::Adt(adt, ..) => {
1350                             if adt.is_enum() {
1351                                 err.span_label(field.ident.span, format!(
1352                                     "`{}::{}` does not have this field",
1353                                     ty,
1354                                     variant.ident
1355                                 ));
1356                             } else {
1357                                 err.span_label(field.ident.span, format!(
1358                                     "`{}` does not have this field",
1359                                     ty
1360                                 ));
1361                             }
1362                             let available_field_names = self.available_field_names(variant);
1363                             if !available_field_names.is_empty() {
1364                                 err.note(&format!("available fields are: {}",
1365                                                   self.name_series_display(available_field_names)));
1366                             }
1367                         }
1368                         _ => bug!("non-ADT passed to report_unknown_field")
1369                     }
1370                 };
1371             }
1372         }
1373         err.emit();
1374     }
1375
1376     // Return an hint about the closest match in field names
1377     fn suggest_field_name(variant: &'tcx ty::VariantDef,
1378                           field: &str,
1379                           skip: Vec<Symbol>)
1380                           -> Option<Symbol> {
1381         let names = variant.fields.iter().filter_map(|field| {
1382             // ignore already set fields and private fields from non-local crates
1383             if skip.iter().any(|&x| x == field.ident.name) ||
1384                (!variant.def_id.is_local() && field.vis != Visibility::Public)
1385             {
1386                 None
1387             } else {
1388                 Some(&field.ident.name)
1389             }
1390         });
1391
1392         find_best_match_for_name(names, field, None)
1393     }
1394
1395     fn available_field_names(&self, variant: &'tcx ty::VariantDef) -> Vec<ast::Name> {
1396         variant.fields.iter().filter(|field| {
1397             let def_scope =
1398                 self.tcx.adjust_ident_and_get_scope(field.ident, variant.def_id, self.body_id).1;
1399             field.vis.is_accessible_from(def_scope, self.tcx)
1400         })
1401         .map(|field| field.ident.name)
1402         .collect()
1403     }
1404
1405     fn name_series_display(&self, names: Vec<ast::Name>) -> String {
1406         // dynamic limit, to never omit just one field
1407         let limit = if names.len() == 6 { 6 } else { 5 };
1408         let mut display = names.iter().take(limit)
1409             .map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
1410         if names.len() > limit {
1411             display = format!("{} ... and {} others", display, names.len() - limit);
1412         }
1413         display
1414     }
1415
1416     // Check field access expressions
1417     fn check_field(
1418         &self,
1419         expr: &'tcx hir::Expr,
1420         needs: Needs,
1421         base: &'tcx hir::Expr,
1422         field: ast::Ident,
1423     ) -> Ty<'tcx> {
1424         let expr_t = self.check_expr_with_needs(base, needs);
1425         let expr_t = self.structurally_resolved_type(base.span,
1426                                                      expr_t);
1427         let mut private_candidate = None;
1428         let mut autoderef = self.autoderef(expr.span, expr_t);
1429         while let Some((base_t, _)) = autoderef.next() {
1430             match base_t.kind {
1431                 ty::Adt(base_def, substs) if !base_def.is_enum() => {
1432                     debug!("struct named {:?}",  base_t);
1433                     let (ident, def_scope) =
1434                         self.tcx.adjust_ident_and_get_scope(field, base_def.did, self.body_id);
1435                     let fields = &base_def.non_enum_variant().fields;
1436                     if let Some(index) = fields.iter().position(|f| f.ident.modern() == ident) {
1437                         let field = &fields[index];
1438                         let field_ty = self.field_ty(expr.span, field, substs);
1439                         // Save the index of all fields regardless of their visibility in case
1440                         // of error recovery.
1441                         self.write_field_index(expr.hir_id, index);
1442                         if field.vis.is_accessible_from(def_scope, self.tcx) {
1443                             let adjustments = autoderef.adjust_steps(self, needs);
1444                             self.apply_adjustments(base, adjustments);
1445                             autoderef.finalize(self);
1446
1447                             self.tcx.check_stability(field.did, Some(expr.hir_id), expr.span);
1448                             return field_ty;
1449                         }
1450                         private_candidate = Some((base_def.did, field_ty));
1451                     }
1452                 }
1453                 ty::Tuple(ref tys) => {
1454                     let fstr = field.as_str();
1455                     if let Ok(index) = fstr.parse::<usize>() {
1456                         if fstr == index.to_string() {
1457                             if let Some(field_ty) = tys.get(index) {
1458                                 let adjustments = autoderef.adjust_steps(self, needs);
1459                                 self.apply_adjustments(base, adjustments);
1460                                 autoderef.finalize(self);
1461
1462                                 self.write_field_index(expr.hir_id, index);
1463                                 return field_ty.expect_ty();
1464                             }
1465                         }
1466                     }
1467                 }
1468                 _ => {}
1469             }
1470         }
1471         autoderef.unambiguous_final_ty(self);
1472
1473         if let Some((did, field_ty)) = private_candidate {
1474             self.ban_private_field_access(expr, expr_t, field, did);
1475             return field_ty;
1476         }
1477
1478         if field.name == kw::Invalid {
1479         } else if self.method_exists(field, expr_t, expr.hir_id, true) {
1480             self.ban_take_value_of_method(expr, expr_t, field);
1481         } else if !expr_t.is_primitive_ty() {
1482             self.ban_nonexisting_field(field, base, expr, expr_t);
1483         } else {
1484             type_error_struct!(
1485                 self.tcx().sess,
1486                 field.span,
1487                 expr_t,
1488                 E0610,
1489                 "`{}` is a primitive type and therefore doesn't have fields",
1490                 expr_t
1491             )
1492             .emit();
1493         }
1494
1495         self.tcx().types.err
1496     }
1497
1498     fn ban_nonexisting_field(
1499         &self,
1500         field: ast::Ident,
1501         base: &'tcx hir::Expr,
1502         expr: &'tcx hir::Expr,
1503         expr_t: Ty<'tcx>,
1504     ) {
1505         let mut err = self.no_such_field_err(field.span, field, expr_t);
1506
1507         match expr_t.peel_refs().kind {
1508             ty::Array(_, len) => {
1509                 self.maybe_suggest_array_indexing(&mut err, expr, base, field, len);
1510             }
1511             ty::RawPtr(..) => {
1512                 self.suggest_first_deref_field(&mut err, expr, base, field);
1513             }
1514             ty::Adt(def, _) if !def.is_enum() => {
1515                 self.suggest_fields_on_recordish(&mut err, def, field);
1516             }
1517             ty::Param(param_ty) => {
1518                 self.point_at_param_definition(&mut err, param_ty);
1519             }
1520             _ => {}
1521         }
1522
1523         if field.name == kw::Await {
1524             // We know by construction that `<expr>.await` is either on Rust 2015
1525             // or results in `ExprKind::Await`. Suggest switching the edition to 2018.
1526             err.note("to `.await` a `Future`, switch to Rust 2018");
1527             err.help("set `edition = \"2018\"` in `Cargo.toml`");
1528             err.note("for more on editions, read https://doc.rust-lang.org/edition-guide");
1529         }
1530
1531         err.emit();
1532     }
1533
1534     fn ban_private_field_access(
1535         &self,
1536         expr: &hir::Expr,
1537         expr_t: Ty<'tcx>,
1538         field: ast::Ident,
1539         base_did: DefId,
1540     ) {
1541         let struct_path = self.tcx().def_path_str(base_did);
1542         let kind_name = match self.tcx().def_kind(base_did) {
1543             Some(def_kind) => def_kind.descr(base_did),
1544             _ => " ",
1545         };
1546         let mut err = struct_span_err!(
1547             self.tcx().sess,
1548             expr.span,
1549             E0616,
1550             "field `{}` of {} `{}` is private",
1551             field,
1552             kind_name,
1553             struct_path
1554         );
1555         // Also check if an accessible method exists, which is often what is meant.
1556         if self.method_exists(field, expr_t, expr.hir_id, false)
1557             && !self.expr_in_place(expr.hir_id)
1558         {
1559             self.suggest_method_call(
1560                 &mut err,
1561                 &format!("a method `{}` also exists, call it with parentheses", field),
1562                 field,
1563                 expr_t,
1564                 expr.hir_id,
1565             );
1566         }
1567         err.emit();
1568     }
1569
1570     fn ban_take_value_of_method(&self, expr: &hir::Expr, expr_t: Ty<'tcx>, field: ast::Ident) {
1571         let mut err = type_error_struct!(
1572             self.tcx().sess,
1573             field.span,
1574             expr_t,
1575             E0615,
1576             "attempted to take value of method `{}` on type `{}`",
1577             field,
1578             expr_t
1579         );
1580
1581         if !self.expr_in_place(expr.hir_id) {
1582             self.suggest_method_call(
1583                 &mut err,
1584                 "use parentheses to call the method",
1585                 field,
1586                 expr_t,
1587                 expr.hir_id
1588             );
1589         } else {
1590             err.help("methods are immutable and cannot be assigned to");
1591         }
1592
1593         err.emit();
1594     }
1595
1596     fn point_at_param_definition(&self, err: &mut DiagnosticBuilder<'_>, param: ty::ParamTy) {
1597         let generics = self.tcx.generics_of(self.body_id.owner_def_id());
1598         let generic_param = generics.type_param(&param, self.tcx);
1599         if let ty::GenericParamDefKind::Type{synthetic: Some(..), ..} = generic_param.kind {
1600             return;
1601         }
1602         let param_def_id = generic_param.def_id;
1603         let param_hir_id = match self.tcx.hir().as_local_hir_id(param_def_id) {
1604             Some(x) => x,
1605             None    => return,
1606         };
1607         let param_span = self.tcx.hir().span(param_hir_id);
1608         let param_name = self.tcx.hir().ty_param_name(param_hir_id);
1609
1610         err.span_label(param_span, &format!("type parameter '{}' declared here", param_name));
1611     }
1612
1613     fn suggest_fields_on_recordish(
1614         &self,
1615         err: &mut DiagnosticBuilder<'_>,
1616         def: &'tcx ty::AdtDef,
1617         field: ast::Ident,
1618     ) {
1619         if let Some(suggested_field_name) =
1620             Self::suggest_field_name(def.non_enum_variant(), &field.as_str(), vec![])
1621         {
1622             err.span_suggestion(
1623                 field.span,
1624                 "a field with a similar name exists",
1625                 suggested_field_name.to_string(),
1626                 Applicability::MaybeIncorrect,
1627             );
1628         } else {
1629             err.span_label(field.span, "unknown field");
1630             let struct_variant_def = def.non_enum_variant();
1631             let field_names = self.available_field_names(struct_variant_def);
1632             if !field_names.is_empty() {
1633                 err.note(&format!(
1634                     "available fields are: {}",
1635                     self.name_series_display(field_names),
1636                 ));
1637             }
1638         }
1639     }
1640
1641     fn maybe_suggest_array_indexing(
1642         &self,
1643         err: &mut DiagnosticBuilder<'_>,
1644         expr: &hir::Expr,
1645         base: &hir::Expr,
1646         field: ast::Ident,
1647         len: &ty::Const<'tcx>,
1648     ) {
1649         if let (Some(len), Ok(user_index)) = (
1650             len.try_eval_usize(self.tcx, self.param_env),
1651             field.as_str().parse::<u64>()
1652         ) {
1653             let base = self.tcx.sess.source_map()
1654                 .span_to_snippet(base.span)
1655                 .unwrap_or_else(|_| self.tcx.hir().hir_to_pretty_string(base.hir_id));
1656             let help = "instead of using tuple indexing, use array indexing";
1657             let suggestion = format!("{}[{}]", base, field);
1658             let applicability = if len < user_index {
1659                 Applicability::MachineApplicable
1660             } else {
1661                 Applicability::MaybeIncorrect
1662             };
1663             err.span_suggestion(expr.span, help, suggestion, applicability);
1664         }
1665     }
1666
1667     fn suggest_first_deref_field(
1668         &self,
1669         err: &mut DiagnosticBuilder<'_>,
1670         expr: &hir::Expr,
1671         base: &hir::Expr,
1672         field: ast::Ident,
1673     ) {
1674         let base = self.tcx.sess.source_map()
1675             .span_to_snippet(base.span)
1676             .unwrap_or_else(|_| self.tcx.hir().hir_to_pretty_string(base.hir_id));
1677         let msg = format!("`{}` is a raw pointer; try dereferencing it", base);
1678         let suggestion = format!("(*{}).{}", base, field);
1679         err.span_suggestion(
1680             expr.span,
1681             &msg,
1682             suggestion,
1683             Applicability::MaybeIncorrect,
1684         );
1685     }
1686
1687     fn no_such_field_err<T: Display>(&self, span: Span, field: T, expr_t: &ty::TyS<'_>)
1688         -> DiagnosticBuilder<'_> {
1689         type_error_struct!(self.tcx().sess, span, expr_t, E0609,
1690                            "no field `{}` on type `{}`",
1691                            field, expr_t)
1692     }
1693
1694     fn check_expr_index(
1695         &self,
1696         base: &'tcx hir::Expr,
1697         idx: &'tcx hir::Expr,
1698         needs: Needs,
1699         expr: &'tcx hir::Expr,
1700     ) -> Ty<'tcx> {
1701         let base_t = self.check_expr_with_needs(&base, needs);
1702         let idx_t = self.check_expr(&idx);
1703
1704         if base_t.references_error() {
1705             base_t
1706         } else if idx_t.references_error() {
1707             idx_t
1708         } else {
1709             let base_t = self.structurally_resolved_type(base.span, base_t);
1710             match self.lookup_indexing(expr, base, base_t, idx_t, needs) {
1711                 Some((index_ty, element_ty)) => {
1712                     // two-phase not needed because index_ty is never mutable
1713                     self.demand_coerce(idx, idx_t, index_ty, AllowTwoPhase::No);
1714                     element_ty
1715                 }
1716                 None => {
1717                     let mut err =
1718                         type_error_struct!(self.tcx.sess, expr.span, base_t, E0608,
1719                                             "cannot index into a value of type `{}`",
1720                                             base_t);
1721                     // Try to give some advice about indexing tuples.
1722                     if let ty::Tuple(..) = base_t.kind {
1723                         let mut needs_note = true;
1724                         // If the index is an integer, we can show the actual
1725                         // fixed expression:
1726                         if let ExprKind::Lit(ref lit) = idx.kind {
1727                             if let ast::LitKind::Int(i, ast::LitIntType::Unsuffixed) = lit.node {
1728                                 let snip = self.tcx.sess.source_map().span_to_snippet(base.span);
1729                                 if let Ok(snip) = snip {
1730                                     err.span_suggestion(
1731                                         expr.span,
1732                                         "to access tuple elements, use",
1733                                         format!("{}.{}", snip, i),
1734                                         Applicability::MachineApplicable,
1735                                     );
1736                                     needs_note = false;
1737                                 }
1738                             }
1739                         }
1740                         if needs_note {
1741                             err.help("to access tuple elements, use tuple indexing \
1742                                         syntax (e.g., `tuple.0`)");
1743                         }
1744                     }
1745                     err.emit();
1746                     self.tcx.types.err
1747                 }
1748             }
1749         }
1750     }
1751
1752     fn check_expr_yield(
1753         &self,
1754         value: &'tcx hir::Expr,
1755         expr: &'tcx hir::Expr,
1756         src: &'tcx hir::YieldSource
1757     ) -> Ty<'tcx> {
1758         match self.yield_ty {
1759             Some(ty) => {
1760                 self.check_expr_coercable_to_type(&value, ty);
1761             }
1762             // Given that this `yield` expression was generated as a result of lowering a `.await`,
1763             // we know that the yield type must be `()`; however, the context won't contain this
1764             // information. Hence, we check the source of the yield expression here and check its
1765             // value's type against `()` (this check should always hold).
1766             None if src == &hir::YieldSource::Await => {
1767                 self.check_expr_coercable_to_type(&value, self.tcx.mk_unit());
1768             }
1769             _ => {
1770                 struct_span_err!(self.tcx.sess, expr.span, E0627,
1771                                     "yield statement outside of generator literal").emit();
1772             }
1773         }
1774         self.tcx.mk_unit()
1775     }
1776 }
1777
1778 pub(super) fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
1779     Some(match ty.kind {
1780         ty::Bool => "true",
1781         ty::Char => "'a'",
1782         ty::Int(_) | ty::Uint(_) => "42",
1783         ty::Float(_) => "3.14159",
1784         ty::Error | ty::Never => return None,
1785         _ => "value",
1786     })
1787 }